This is a little system I put together for fast rendering of mirrors for
(limited circumstance) in-game use. It's very simple indeed, but I don't
recall seeing anything quite like it until the shots of Super Mario
Sunshine, so I just had to figure it out (I've been trying for ages, and
finally got it just about right -- it's the positioning/zooming code that
was that hard part).
Each mirror has an associated camera, which is positioned 'opposite' the
main viewing camera behind the mirror, and simply renders its view to the
back buffer. This is then copied into the mirror's texture. Mirrors only
render when the main camera is within a certain range, so they only affect
frame rates when you can see them. There are a couple of limitations:
You can't have anything behind the mirror; not a problem if your level is
designed around this (eg. a single-sided wall behind the mirror is fine,
since its back can't be seen by the mirror's camera);
Anyway, it runs very well on modern machines (eg Geforce2/3 and up), and not
too badly on low end (ATI Rage). It was developed on an ATI laptop, where it
ran quite acceptably, but I've put frame-tweening code in for this public
release, so it skips frames there :)
It's not 100% physically correct, so you get 'flattening' at shallow
angles (which is avoided by the tried and tested method of... limiting where
the player can go :)
It's limited to the size of the display mode here, since it renders to the
back buffer (eg. asking or a 512 x 512 texture on a 640 x 480 screen will
fail, though this example automatically creates a smaller texture). Bear
this in mind when running the demo.
Try it out here...
(Use cursors plus A and Z to move around; the mirror will follow you. Click
and drag the mirror to move it manually.)
Mail me if you need to know any more about it!